This invention is concerned with improvements in a fluid bellows controlled pressure relay of a type designed to operate an alarm switch in response to a sudden rise in the internal pressure developing in a tank with which the relay is associated.
The relay is especially suited for use as a protective device for a fluid cooled electrical transformer apparatus so as to sense development of an abnormal pressure rise in the apparatus, and to issue a warning signal that would require an attendant to inspect the apparatus for the cause of the pressure rise.
A feature of the invention lies in the particular organization of its components whereby its operation is reliable in areas subject to strong vibrations and shock such as may occur under seismic conditions.
In accordance with the invention, there is provided a fluid bellows controlled pressure relay comprising a housing having a lower open end adapted to be mounted over a complementary opening in a pressure developing tank, a bellows support block mounted in the housing, a pressure sensing bellows mounted to an underside of the block having a bottom end adapted to be subjected to pressures applied through said lower open end, a second vertically extending bellows mounted to an upper surface of the block, a third bellows mounted to the upper surface of the block in spaced parallel relation to the second bellows, the interiors of the several bellows being connected in communication with a common channel in the block, the channel and connected bellows defining a closed hydraulic circuit filled with fluid, a switch having a push-pin switch contact in an electrical alarm circuit, a bracket pivoted intermediately of its ends to a stationary support and supported in a balanced condition at its ends upon the second and third bellows, a switch actuating element carried by the bracket disposed in the balanced condition of the bracket in ineffective abutting relation to the push-pin switch contact, the second bellows having an orifice communicating its interior with the common channel, and the third bellows having a relatively larger port communicating its interior with the common channel, the sensing bellows being contractible upon sensing pressure variations applied through said lower open end to force fluid from the channel to the orifice and larger port respectively of the second and third bellows, the second bellows having a larger diameter area subject to pressures from the channel fluid entering the orifice than the third bellows has subject to pressure from the channel at the larger port, the second and third bellows being responsive to normal pressure changes from the channel in such manner as to maintain the bracket in neutral position whereby the switch actuating element will not actuate the push-pin switch contact, and the second and third bellows being responsive to sudden pressure changes from the channel in such manner that the bracket is caused to swing about its pivot to cause the switch actuating element to actuate the push-pin switch contact.